As light output from LEDs or solid state light sources improve quickly and become increasingly viable alternatives, conventional lightings such as incandescent lamps and fluorescent lamps will soon be replaced with energy-efficient LEDs. A conventional LED is small and energy efficient with a good lifetime. Various commercial applications of LEDs, such as traffic lights, automobile lightings, and electronic billboards, have already been placed in service.
An important aspect of solid state optical property in applying general illumination is total luminous flux, or overall visible lighting output. A problem associated with lighting output from a solid state light emitter or LED is the total internal reflection (“TIR”) phenomenon. When a light ray or beam crosses between two different materials with two different medium having different refractive indices, the TIR phenomenon occurs. For instance, when light ray strikes boundaries between two layers having different materials with different refractive indices, the light ray may be partially refracted at the boundary surface, and partially reflected through a layer.
The occurrence of the TIR phenomena within solid state lighting devices normally impacts and reduces luminous efficiency. In some instances, the TIR phenomena can generate heat from the reflective light. For example, when the blue optical light generated by LED strikes at an area of relatively flat surface of a phosphor layer, a TIR phenomenon between the phosphor layer and the LED may occur depending on the angle of the optical light with respect to the surface of the phosphor layer.